1. Field of the Invention
The present invention relates to a heating method and a heating apparatus for a band-shaped body. The invention particularly relates to a heating method and heating apparatus that heat and dry a coating liquid applied to a band-shaped body in such a way as to enable a temperature history of the band-shaped body to be practically uniform on both upstream and downstream sides of a joint portion passing through, at which joint portion two band-shaped bodies with at least one of different widths or different thicknesses are joined.
2. Description of the Related Art
Planographic printing plates, silver salt films such as photographic films and cinefilms, photographic paper, and magnetic recording materials such as audio tapes, video tapes, base films of floppy (registered trademark) discs are manufactured in the following manner. While a band-shaped body such as a support web, a base film, or baryta paper is conveyed in a constant direction, a coating liquid such as a photosensitive layer forming liquid, a heat-sensitive layer forming liquid, a photosensitive emulsion, or a magnetic layer forming liquid is applied to the band-shaped body. This coating is then dried and then the dried band-shaped body is cut into predetermined sizes to suit.
The following examples of drying methods and drying devices for drying the coating liquid applied to the band-shaped body are proposed:
a method for drying a photographic photosensitive band-shaped material in which a band-shaped material to which a coating liquid including an organic solvent is applied is continuously conveyed, the coating liquid is dried to touch-dry at a temperature of 150 to 190% and air stream velocity of 3 to 30 m/s, and then residual solvent in the coating film is evaporated by a heating roll (Japanese Patent Publication (JP-B) No. 6-49175);
a band-shaped material drying device including a heating roll arranged so as to be capable of contacting with the conveyed band-shaped material, a swing roll that determines a contact angle between the heating roll and the band-shaped material, and a swing roll moving unit that moves the swing roll so that the contact angle changes according to a thickness of the band-shaped material (U.S. Pat. No. 2,530,219);
a planographic printing plate manufacturing method including drying and heating consisting of: continuously conveying a band-shaped support member while applying a photosensitive coating liquid including an organic solvent, forming a photosensitive coating layer; drying the photosensitive coating layer to touch-dry using a first heating unit; and heating the support member and the photosensitive coating layer using a second heating unit provided downstream of the first heating unit, so as to accelerate hardening of the photosensitive coating layer (Japanese Patent Application Laid-Open (JP-A) No. 2002-14461); and
a planographic printing plate drying device including: an energy applying unit that applies energy for drying a coating liquid of a moving planographic printing plate; a temperature measuring device that is arranged downstream of an area in which the energy is applied by the energy applying unit, and measures the temperature of the planographic printing plate; and an adjusting unit that adjusts the amount of the energy to be applied by the energy applying unit to the planographic printing plate according to the temperature of the planographic printing plate measured by the temperature measuring device (JP-A No. 2003-98685).
In recent years, in addition to so-called conventional printing plates such as conventional type PS plates, Computer to Plate printing plates, where printing images are directly written thereon by a laser beam based on image data from a computer, have become widely used.
In general, when a support web is switched during the manufacturing of planographic printing plates, an end of one support web is joined to another support web with a different width or different thickness. Since the width or the thickness of the support web changes at the joint portion, thermal capacity of the support web also changes at the joint portion. Therefore if the quantities of heat supplied to the support web are the same on each (upstream, downstream) side of the joint portion then a difference in the temperature history of the support web will arise in the vicinity of the joint portion.
With conventional printing plates, the influence, on quality, of differences in the temperature history in the drying step after the photosensitive layer forming liquid is applied to the support web is comparatively small. For this reason, when conventional printing plates are produced under constant drying conditions, variations in quality due to changes in the quantity of heating of the photosensitive layer caused by the change in thermal capacity of the support web fall within acceptable tolerances.
With Computer to Plate (CTP) printing plates, however, since the influence of drying temperature history on quality is greater than with conventional printing plates, it is necessary to set the drying conditions according to the thickness of the support web. When a support web having non-uniform thickness is continuously driven, it is necessary to change the drying conditions at the joint portion.
When, however, the drying condition is changed, a certain time is required until the drying conditions become stable. For this reason, during the interval from the time when the drying conditions are changed to the time when the drying conditions become stable, the quality cannot be guaranteed, resulting in considerable waste.
It follows that when CTP printing plates having a support web with a certain thickness are manufactured, followed by production of CTP printing plates having a different thickness of support web, dummy plates have to be inserted or the line has to be stopped so that the drying conditions can be changed. Manufacturing of the CTP plates having the different support web thickness can then start.
For this reason, manufacturing productivity for CTP plates is significantly lower than that of conventional printing plates.